Assessment of a Plan for U.S. Participation in Euclid (2012) / Chapter Skim
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2 Findings
Pages 4-10
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From page 4... ...
The statistical power of this technique to probe dark energy derives from the ability to measure cosmic shear in tomographic redshift slices. To maximize weak gravitational lensing signal-to-noise, Euclid visual imaging will be carried out in a single, broad optical band.
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The Euclid Wide Survey is expected to cover a larger area than will the WFIRST survey. The Euclid surveys will be unprecedented, producing a massive data set of deep images and spectra covering a significant fraction of the sky.
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If limited by statistical errors, then the expected weak gravitational lensing dark energy science return will be somewhat greater from Euclid than WFIRST.17 The weak gravitational lensing signal is very subtle, however, and its detection is vulnerable to systematic errors introduced by the instrument,18 by the atmosphere (when observed from the ground) , and by astrophysical effects such as intrinsic alignments.19 The WFIRST multiband approach to weak gravitational lensing is more robust than Euclid's single very broad band, which is potentially vulnerable to galaxy color gradients.20,21 Because WFIRST measures lensing in three passbands, its data can be internally cross-correlated to help mitigate systematic measurement error.
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From page 7... ...
In the same timeframe as Euclid and WFIRST, LSST should also carry out its deeper optical survey. There are clear, but notably asymmetric, potential synergies between these projects and Euclid: multiband optical data from the ground are necessary for Euclid to meet its weak gravitational lensing science requirements; on the other hand, while Euclid data would enhance the science reach of the ground-based surveys, those data are not seen as necessary to achieving the primary science goals of those surveys.
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From page 8... ...
LSST, Euclid's broad band optical images, and WFIRST deep survey will be able to see fainter galaxies than Euclid's wide survey. The WFIRST deep survey goes deeper, but the Euclid survey covers a much larger area.
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From page 9... ...
manufactured filter wheel, based on technologies developed for the Hubble Space Telescope, would enable the Euclid telescope to continue its optical observations while the infrared filters are being switched. Reaction wheels would provide enhanced guiding and stabilization for the Euclid spacecraft, compared with the current mission specification of using cold gas thrusters.
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From page 10... ...
Dr. Hertz also stated that expenditure of these funds on Euclid hardware would not impact the launch schedule for WFIRST, since according to current NASA budget projections significant expenditure on the WFIRST mission would only commence in the 2017-2018 timeframe, when JWST construction spending rolls off.
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